Well here is my F5, i actually built this for a friend last year which he has been running all this time no problems to my excitement he told me he wants to upgrade and buy something he can have insurance on so we went looking for amps and so far he has decided on a couple of "class-A" Accuphase amps lucky bugger!

anyway this was my third Nelson Pass amp and definitely the best sounding, although the Zen V4 sounded great too! this F5 beats it for me.

Originally applied too much thermal paste, started again took layers off the mica so that the mica was very thin, then added minimal paste. worked wonders on the heat transfer!
before then i had no idea you could split the mica with a sharp knife2.jpg

In total I think it cost us about £300-350 to make im buying it back off him for £200 which is nice i shall enjoy the sound when it arrives back here.
I do have one question, there are capacitors on my board! but none on the original F5 any comments on that ?

Well There we go, if theres anything you think i could improve on let me know thx

Do you think it would be possible to have some kind of Bias adjustment so that i can put the amp in power saving mode for low listening levels, then hit the bias on full if i turn the music up ? either variable or switched bias. how easy do u experts think that would be to do ?

Also i don't have a pre-amp and use mainly the computer for volume, has anyone else just attached a volume to the amp ? or are u all using pre-amps

Yeah, i might get the proper boards, but then un-soldering the components and putting them on the new board is a bit time consuming, could just buy some new components, decisions decisions

Nah, that would open a can of worms. Just get approved boards for the next one.

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Do you think it would be possible to have some kind of Bias adjustment so that i can put the amp in power saving mode for low listening levels, then hit the bias on full if i turn the music up ? either variable or switched bias.

The F5 is one big balancing act... that might upset the balance in weird ways... I wouldn't do it, but would be interested in seeing what the smart people have to say about it.

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Also i don't have a pre-amp and use mainly the computer for volume, has anyone else just attached a volume to the amp ? or are u all using pre-amps

Works fine. You might not have enough gain, depending on your soundcard or headphone jack, but that's easy enough to test, and if you find you need a bit more gain, quite easy to change in the F5.

Nah, that would open a can of worms. Just get approved boards for the next one.

The F5 is one big balancing act... that might upset the balance in weird ways... I wouldn't do it, but would be interested in seeing what the smart people have to say about it.

Works fine. You might not have enough gain, depending on your soundcard or headphone jack, but that's easy enough to test, and if you find you need a bit more gain, quite easy to change in the F5.

Thanks, With the Zen v4 i did make a switch that would change the value of the bias resistor. In on position is added another resistor in parallel with the bias one to give it full value. it seemed to work well, hitting the switch produced a very small audible click but seemed harmless .

But i see F5 i remember now the bias is kind of auto biasing with thermistors and a bit more complicated.

About the volume, what i meant with that is, i use computer for volume but realy it would be better to have the computer volume level set to max and build a volume into the amp ? apparently digital sounds worse the lower the output from soundcard.
also if i accidentally unplug/nock the jack lead to the amp from my laptop (source) when its on it will probably give a very loud buzz on the speakers.

For anyone wondering the F5 is loud enough without a pre-amp connected to the average computer sound card, Iv'e not tested CD-players yet

i had nothing to to with the design. i only gave him the calculation for the cascoding resistors. this is the same boards that i have. but my Boards are not cascoded.

Allright, Audiosan. So my quest remains: Has anyone actually built cvillers ver.2 in the cascoded option ?
Since you calculated the resistors, do you have an idea of the values for C101/102 ? They are absent from the BOM. But clearly actached to the cascoding transistors/resistors. (Ironic really, Mr. Pass made a point of avoiding capators...;-)

i had nothing to to with the design. i only gave him the calculation for the cascoding resistors. this is the same boards that i have. but my Boards are not cascoded.

Sorry, me again, regarding cascoding resistors. I just noticed that the diyAudio store F5c (based on cviller design, but new board) changed the schematic for these voltage deviding resistors.
Your design was 4K7 for R101 thru 104.
They changed it to 10 ohms for R 101 thru 104 ! That's gotta be an error !
Why pull 1 amp just for the bases of the cascode resistors ?
I guess I should stick to 4K7, right ?
(They also made the emitter resistors in half without changing the current sensing circuit. So now these limit at 20 amps for EACH O/P device....).
(I should say at this point that I dont want to use dual parallel O/P devices in my build, just the input cascoding which I expect will help to reduce distortion. I learned long ago that it is difficilt to parallel semiconductors. The hottest one will carry the load. Unless you use large emitter resistors, which is not were you wanna move).
Schematics in the attachment and here:http://www.diyaudio.com/forums/blogs...e_forguide.png

Allright, Audiosan. So my quest remains: Has anyone actually built cvillers ver.2 in the cascoded option ?
Since you calculated the resistors, do you have an idea of the values for C101/102 ? They are absent from the BOM. But clearly actached to the cascoding transistors/resistors. (Ironic really, Mr. Pass made a point of avoiding capators...;-)

you can use 10-47uF for those caps. regarding the resistors, the value depends on the rail voltage. if all 4 resistors are of the same value, the voltage will be little under half of the rail voltage.